The objective of the proposed studies is to investigate the mechanisms which may underlie the asynchronous increase in rate and depth of respiration following a sudden change of inspired O2 or CO2 concentration. A conscious-dog preparation will be employed in the proposed studies. Dogs will be trained to lie quietly in place, and surgically prepared with permanent tracheostomy and exteriorized vagal loops. Breath-by-breath response of ventilation, tidal volume, and respiratory rate to transient hypercapnia, transient hypoxia, steady-state hypercapni, and steady-state hypoxia will be determined in each dog. Breathing pattern responses will be quantified by analyzing the relationship between ventilation and tidal volume, and compared between the transient and steady-state responses. The possible roles of different groups of chemoreceptors, distinguished by their different responding rates to the stimulus, in causing the gradual change of breathing pattern following the onset of these stimuli may thus be examined. To differentiate the relative contribution of vagal volume-feedback and non-vagal factors in regulating the breathing pattern of both transient and steady-state responses, studies described above will be repeated after both vagus nerves are blocked by cooling. To evaluate the role of bronchomotor tone, the studies will also be repeated when the change in bronchomotor tone is prevented by atropine. Results of these studies may provide more quantitative information and contribute to a better understanding of the overall regulation of breathing pattern response to these chemical stimuli.